Cu Core Ball, Solder Joint, Solder Paste and Formed Solder

ABSTRACT

The Cu core ball contains a Cu ball and one or more metal layer for covering a surface of the Cu ball, each layer including one or more element selected from Ni, Co, Fe and Pd. The Cu ball contains at least one element selected from Fe, Ag, and Ni in a total amount of 5.0 or more to 50.0 ppm by mass or lower, S in an amount of 0 ppm by mass or more to 1.0 ppm by mass or lower, P in an amount of 0 ppm by mass or more to less than 3.0 ppm by mass, and remainder of Cu and inevitable impurities. The Cu ball contains purity which is 99.995% by mass or higher and 99.9995% or lower, sphericity which is 0.95 or higher and a diameter of 1 μm or more to 1000 μm or lower.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application JP2018-111872 filed Jun. 12, 2018, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a Cu core ball in which a metallayer(s) cover(s) a Cu ball, a solder joint using the Cu core ball,solder paste using the same and formed solder using the same.

Description of Related Art

Recently, along development of compact information equipment, electroniccomponents to be mounted have been downsized rapidly. A ball grid alley(hereinafter referred to as “BGA”) having electrodes at its rear surfacehas been applied to such electronic components in order to cope with anarrowed connection terminal and a reduced mounting area because of thedownsizing requirement.

As the electronic components to which the BGA is applied, for example, asemiconductor package is exemplified. In the semiconductor package,semiconductor chips having electrodes are sealed with resin. Solderbumps are formed on the electrodes of the semiconductor chips. Thissolder bump is formed by joining a solder ball to an electrode of thesemiconductor chip. The semiconductor package to which the BGA isapplied is mounted on a printed circuit board by joining the solder bumpmelted by the heating to a conductive land of the printed circuit board.Additionally, a three-dimensional high-density mounting structure hasbeen studied by stacking up the semiconductor packages in a heightdirection in order to meet the further high-density mountingrequirement.

Such a high-density mounting structure of the electronic components,however, may cause any soft errors in which memory contents arerewritten when alpha rays enter into a memory cell of a semiconductorintegral circuit (IC). Accordingly, solder materials with low alpha raysor a Cu ball with low alpha rays, which has decreased contents of aradioisotope, have been recently developed. Japanese Patent No. 5435182discloses a Cu ball with low alpha rays, which contains Pb and Bi andhas a purity which is 99.9% or higher to 99.995% or lower. JapanesePatent No. 5585751 discloses a Cu ball that has a purity which is 99.9%or higher to 99.995% or lower, has sphericity which is 0.95 or higherand has the Vickers hardness which is 20 HV or higher to 60 HV or lower.

By the way, since the Vickers hardness of the Cu ball is large when itscrystal grains is fine, its durability against external stress is madeinferior and its impact resistance to dropping is also deteriorated.Therefore, any predetermined softness, namely, the Vickers hardnesswhich is equal to or lower than a predetermined value thereof may berequired for the Cu ball to be used for mounting the electroniccomponents.

For manufacturing the soft Cu ball, it is a general practice to increasepurity of Cu. This is because the crystal grains grow up largely whenthere is a small amount of impurity elements since the impurity elementsfunction as a crystal core in the Cu ball, so that the Vickers hardnessof the Cu ball decreases. When increasing the purity of the Cu ball,however, the sphericity of the Cu ball decreases.

In a case of low sphericity of the Cu ball, there may be cases where aself-alignment property of the Cu balls cannot be possibly maintainedwhen the Cu balls are installed on the electrodes and unevenness inheights of the Cu balls occur when mounting a semiconductor chip,thereby causing any bonding defect.

Japanese Patent No. 6256616 discloses a Cu ball that contains Cuexceeding 99.995% by mass, has a total amount of P and S which is 3 ppmby mass or higher to 30 ppm by mass or lower and has a preferablesphericity and Vickers hardness.

SUMMARY OF THE INVENTION

It, however, has been newly founded that a Cu ball containing at least apredetermined amount of S forms a sulfide or a sulfur oxide when heatingthe ball so that it is easy to discolor. The discoloration of the Cuball may cause the wettability thereof to deteriorate and thedeterioration of the wettability may lead to a generation of a conditionthat is not wetted or cause a self-alignment property thereof todeteriorate. Thus, since, in the Cu ball which is easy to discolor, forexample, an adhesion between a surface of the Cu ball and a metal layerbecomes worse and the metal layer has a high oxidizable surface or asurface with high reactivity, such a Cu ball is not suitable for beingcoated by the metal layer. On the other hand, when a sphericity of theCu ball is low, a sphericity of a Cu core ball in which the metal layercovers the Cu ball is also low.

Accordingly, in order to address the above-described issues, the presentinvention has an object to provide a Cu core ball in which the metallayer covers a Cu ball which realizes a high sphericity and a lowhardness and suppresses the discoloration, a solder joint using the Cucore ball, solder paste using the same and formed solder using the same.

To achieve the above-mentioned object, a Cu core ball contains a Cuball, and one or more metal layer for covering a surface of the Cu ball.Each layer includes one or more element selected from a group of Ni, Co,Fe and Pd. The Cu ball contains at least one element selected from agroup of Fe, Ag and Ni in a total amount of 5.0 ppm by mass or more to50.0 ppm by mass or lower, S in an amount of 0 ppm by mass or more to1.0 ppm by mass or lower, P in an amount of 0 ppm by mass or more toless than 3.0 ppm by mass, and remainder of Cu and inevitableimpurities. The Cu ball contains purity which is 99.995% by mass orhigher to 99.9995% by mass or lower, and sphericity which is 0.95 orhigher. The Cu ball contains a diameter of 1 μm or more to 1000 μm orlower. The Cu core ball further contains a solder layer which covers asurface of the metal layer wherein the sphericity thereof is 0.95 orhigher.

A solder joint, solder paste and formed solder respectively use theabove Cu core balls.

According to the present invention, the Cu ball having a high sphericityand a low hardness is realized and the discoloration thereof issuppressed. It is capable of realize a high sphericity of the Cu coreball in which a metal layer covers the Cu ball by realizing the highsphericity of the Cu ball. It is possible to maintain a self-alignmentproperty when installing the Cu core balls on the electric electrodesand to prevent the Cu core balls from varying in the heights thereof. Inaddition, it is capable of improving impact resistance to dropping inthe Cu core ball in which a metal layer covers the Cu ball by realizingthe low hardness of the Cu ball. Further, since the discoloration of theCu ball is suppressed, it is possible to prevent the Cu ball from beingadversely affected by any sulfide or sulfur oxide, thereby beingsuitable for being coated by the metal layer and improving a wettabilitythereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and attainments of the present invention will be becomeapparent to those skilled in the art upon a reading of the followingdetailed description when taken in conjunction with the drawing.

FIG. 1 is a diagram of a Cu core ball according to a first embodiment ofthe prevent invention for illustrating a configuration example thereof.

FIG. 2 is a diagram of a Cu core ball according to a second embodimentof the prevent invention for illustrating a configuration examplethereof.

FIG. 3 is a diagram of an electronic component using the Cu core ballaccording to the first embodiment of the prevent invention forillustrating a configuration example thereof.

FIG. 4 is a diagram of an electronic component using the Cu core ballaccording to the second embodiment of the prevent invention forillustrating a configuration example thereof.

FIG. 5 is a graph showing a relationship between lightness and heatingtime when heating the Cu balls of Executed Examples and ComparisonExamples at 200 degrees C.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe the present invention in detail. In thisspecification, units (such as ppm, ppb and %) relating to composition inthe metal layer of the Cu core ball represent ratios to mass of themetal layer (ppm by mass, ppb by mass and % by mass) unless otherwisespecified. In addition, units (such as ppm, ppb and %) relating tocomposition of the Cu ball represent ratios to mass of the Cu ball (ppmby mass, ppb by mass and % by mass) unless otherwise specified.

FIG. 1 shows a configuration example of a Cu core ball 11A according toa first embodiment of the prevent invention. As shown in FIG. 1, the Cucore ball 11A contains a Cu ball 1 and one or more metal layer 2 forcovering a surface of the Cu ball 1, each layer including one or moreelement selected from the group of Ni, Co, Fe and Pd.

FIG. 2 shows a configuration example of a Cu core ball 11B according toa second embodiment of the prevent invention. As shown in FIG. 2, the Cucore ball 11B contains a Cu ball 1, one or more metal layer 2 thatcovers a surface of the Cu ball 1, each layer including one or moreelement selected from the group of Ni, Co, Fe and Pd and a solder layer3 that covers a surface of the metal layer 2.

FIG. 3 shows a configuration example of an electronic component 60 inwhich a semiconductor chip 10 is mounted on a printed circuit board 40using the Cu core ball 11A according to the first embodiment of theprevent invention. As shown in FIG. 3, the Cu core ball 11A is installedon an electrode 100 of the semiconductor chip 10 via solder paste 12. Inthis example, a structure in which the Cu core ball 11A is installed onthe electrode 100 of the semiconductor chip 10 is called a solder bump30A. Solder paste 42 is printed on an electrode 41 of the printedcircuit board 40. The solder bump 30A of the semiconductor chip 10 isconnected on the electrode 41 of the printed circuit board 40 via thesolder paste 42. In this example, a structure in which the solder bump30A is mounted on the electrode 41 of the printed circuit board 40 iscalled a solder joint 50A.

FIG. 4 shows a configuration example of an electronic component 60 inwhich a semiconductor chip 10 is mounted on a printed circuit board 40using the Cu core ball 11B according to the second embodiment of theprevent invention. As shown in FIG. 4, the Cu core ball 11B is installedon an electrode 100 of the semiconductor chip 10 by applying flux to theelectrode 100 of the semiconductor 10 to wetly spread out the moltensolder layer 3. In this example, a structure in which the Cu core ball11B is installed on the electrode 100 of the semiconductor chip 10 iscalled a solder bump 30B. The solder bump 30B of the semiconductor chip10 is connected on the electrode 41 of the printed circuit board 40 viathe molten solder layer 3 or the solder paste applied to an electrode41. In this example, a structure in which the solder bump 30B is mountedon the electrode 41 of the printed circuit board 40 is called a solderjoint 50B.

In each of the Cu core balls 11A, 11B of the embodiments, the Cu ball 1contains at least one element selected from a group of Fe, Ag and Ni ina total amount of 5.0 ppm by mass or more to 50.0 ppm by mass or lower,S in an amount of 0 ppm by mass or more to 1.0 ppm by mass or lower, Pin an amount of 0 ppm by mass or more to less than 3.0 ppm by mass, andremainder of Cu and inevitable impurities. The Cu ball contains puritywhich is 99.995% (4N5) by mass or higher to 99.9995% (5N5) by mass orlower, and sphericity which is 0.95 or higher.

In the Cu core ball 11A of the first embodiment of the presentinvention, the high sphericity of the Cu ball which the metal layer 2covers enables the sphericity of the Cu core ball 11A to be increased.In the Cu core ball 11B of the second embodiment of the presentinvention, the high sphericity of the Cu ball which the metal layer 2and the solder layer 3 cover also enables the sphericity of the Cu coreball 11B to be increased. The following will describe a preferredembodiment of the Cu ball 1 constituting each of the Cu core balls 11A,11B.

<Sphericity of Cu Ball: 0.95 or Higher>

In the present invention, the sphericity represents a gap from a truesphere. The sphericity is an arithmetic mean value calculated bydividing a diameter of each of 500 Cu balls by a length of the longestaxis of each Cu ball. When a value thereof is closer to the upper limit1.00, this is closer to the true sphere. The sphericity can bedetermined by various kinds of methods, for example, a least squarescenter method (LSC method), a minimum zone center method (MZC method), amaximum inscribed center method (MIC method), a minimum circumscribedcenter method (MCC method), etc. In this invention, the length of thediameter and the length of the longest axis are referred to as lengthsmeasured by measuring equipment, ultra-quick vision, ULTRA QV 350-PROmanufactured by Mitsutoyo Corporation.

For the Cu ball 1, the sphericity is preferably 0.95 or higher, in termsof maintaining an appropriate space between the substrates, is morepreferably 0.98 or higher, and is most preferably 0.99 or higher. Whenthe sphericity of the Cu ball 1 is less than 0.95, the Cu ball 1 becomesan indeterminate shape. Therefore, bumps having uneven heights areformed at the bump formation time and the possibility that poor jointsoccur is increased. When the sphericity is 0.95 or higher, it ispossible to restrain variation of the heights in the solder joints 50A,50B because the Cu ball 1 does not melt at a soldering temperature.Therefore, it is surely possible to prevent the poor joints between thesemiconductor chip 10 and the printed circuit board 40 from occurring.

<Purity of Cu Ball: 99.995% by Mass or Higher to 99.9995% by Mass orLower>

Cu having lower purity generally has higher sphericity, as compared withthe Cu having higher purity, because such Cu having lower purity cancontain any impurity elements which form a crystal core of the Cu ball1. On the other hand, the Cu ball 1 having reduced purity has poorelectric conductivity and thermal conductivity. In addition, a Cu ballusing Cu having higher purity has a low hardness.

Accordingly, when the purity in the Cu ball 1 is 99.995% (4N5) by massor higher to 99.9995% (5N5) by mass or lower, a sufficient sphericity ofthe Cu ball 1 can be maintained. In addition, when the purity in the Cuball 1 is within this range, the alpha dose is sufficiently decreasedand the degradation of the electrical conductivity and thermalconductivity of the Cu ball 1 based on the reduced purity is alsosuppressed.

When manufacturing the Cu ball 1, the Cu material is formed into apredetermined shaped chip and is melted by heating. The molten Cu thenbecomes a spherical form with its surface tension. It is solidified byrapid cooling to become the Cu ball 1. At a process of solidifying themolten Cu from its liquid state, a crystal grain grows up in the moltenCu of the spherical form. In this process, if there are a lot ofimpurity elements, they become the crystal cores and prevent the crystalgrain from growing. Accordingly, the molten Cu of the spherical formbecomes the Cu ball 1 having the high sphericity with the fine crystalgrains that are prevented from growing up. On the other hand, if thenumber of impurity elements is less, then the crystal cores arerelatively less formed. They grow up in a directional property withoutsuppressing the grain growth. As a result thereof, a part of the surfaceof the molten Cu with the spherical form protrudes and solidifies. Thesphericity of such a Cu ball 1 is low. It is conceivable that theimpurity elements may be Fe, Ag, Ni, P, S, Sb, Bi, Zn, Al, As, Cd, Pb,In, Sn, Au, U, Th, etc.

The following will describe the purity of the Cu ball 1 and contents ofthe impurities that limits the sphericity.

<Total Amount of at Least One Element Selected from a Group of Fe, Agand Ni: 5.0 ppm by Mass or More to 50.0 ppm by Mass or Lower>

It is preferable that a total amount of at least one element selectedfrom the impurity elements, particularly Fe, Ag and Ni among theimpurity elements contained in the Cu ball 1 is within a range from 5.0ppm by mass or more to 50.0 ppm by mass or lower. Namely, whencontaining any one of Fe, Ag and Ni, it is preferable that content ofsuch one element is within a range from 5.0 ppm by mass or more to 50.0ppm by mass or lower. When containing any two or more elements of Fe, Agand Ni, it is preferable that contents of such two or more elements arewithin a range from 5.0 ppm by mass or more to 50.0 ppm by mass orlower. Since Fe, Ag and Ni become crystal cores in a melting step of themanufacturing steps of the Cu ball 1, the Cu ball 1 having highsphericity can be manufactured if the Cu contains at least apredetermined amount of Fe, Ag or Ni. Therefore, at least any oneelement of Fe, Ag and Ni is an important element for estimating contentsof impurity elements. In addition, a total amount of at least oneelement selected from a group of Fe, Ag and Ni in a range of 5.0 ppm bymass or more to 50.0 ppm by mass or lower enables discoloration of theCu ball 1 to be suppressed and enables any desired Vickers hardness ofthe Cu ball 1 to be realized, even when not performing any annealingstep to recrystallize the Cu ball 1 slowly by slow cooling after the Cuball 1 is slowly heated.

<Content of S: 0 ppm by Mass or More to 1.0 ppm by Mass or Lower>

Since the Cu ball 1 containing at least a predetermined amount of Sforms a sulfide or a sulfur oxide when heating the ball so that it iseasy to discolor and the wettability thereof deteriorates, the contentof S may be required to be within a range from 0 ppm by mass or more to1.0 ppm by mass or lower. The more the Cu ball 1 has many sulfides orsulfur oxides formed, the lightness of a surface of the Cu ball becomesdark. Therefore, when a measurement result of the lightness of thesurface of the Cu ball indicates a predetermined value or less, it isdetermined that the formation of the sulfide or the sulfur oxide issuppressed and the wettability thereof is good, which will be describedlater.

<Content of P: 0 ppm by Mass or More and Less than 3.0 ppm by Mass>

P may be changed to phosphoric acid and a Cu complex, so that it mayexert a bad influence upon the Cu ball 1. Since the Cu ball containing apredetermined amount of P has high hardness, it is preferable that thecontent of P is 0 ppm by mass or more and less than 3.0 ppm by mass. Itis more preferable that the content of P is less than 1.0 ppm by mass.

<Other Impurity Elements>

The impurity elements contained in the Cu ball 1 such as Sb, Bi, Zn, Al,As, Cd, Pb, In, Sn, Au and the like other than the above-mentionedimpurity elements (hereinafter, referred to as “other impurityelements”) have preferably respective contents which are 0 ppm by massor more and less than 50.0 ppm by mass.

In addition, as described above, the Cu ball 1 contains at least oneelement selected from a group of Fe, Ag and Ni as a necessary element.Since the Cu ball 1, however, cannot prevent any elements other than Fe,Ag and Ni from mixing thereto considering the current technology, the Cuball 1 substantially contains any other impurity elements than Fe, Agand Ni. Note, however, that when the contents of the other impurityelements is less than 1 ppm by mass, any effect or influence by theaddition of each element is hard to appear. In addition, when theelements contained in the Cu ball are analyzed but the contents of theother impurity elements are less than 1 ppm by mass, such a value is anundetectable one of the analyzer. Therefore, when a total amount of atleast one element selected from a group of Fe, Ag and Ni is 50 ppm bymass and the contents of the other impurity elements are less than 1 ppmby mass, it is estimated that the purity of the Cu ball 1 issubstantially 99.995% (4N5) by mass. Further, when a total amount of atleast one element selected from the group of Fe, Ag and Ni is 5 ppm bymass and the contents of the other impurity elements are less than 1 ppmby mass, it is estimated that the purity of the Cu ball 1 issubstantially 99.9995% (5N5) by mass.

<The Vickers Hardness of Cu Ball: 55.5 HV or Lower>

The Vickers hardness of the Cu ball 1 is preferably 55.5 HV or lower.This is because the durability against external stress becomes low, theimpact resistance to dropping gets worse, and cracks are generatedeasily, in a case where the Vickers hardness is large. This is alsobecause, in a case where the auxiliary force such as pressurization isapplied when forming three-dimensional mounting bumps and joints, thereis a possibility that a crash of electrode and the like may occur withthe use of a hard Cu ball. Moreover, this is because, in a case wherethe Vickers hardness of Cu ball 1 is large, a crystal grain becomessmaller than a certain size and therefore, a deterioration of electricalconductivity may be caused. When the Vickers hardness of the Cu ball 1is 55.5 HV or lower, the impact resistance to dropping is satisfactory,cracks are suppressed, a crash of electrode and the like is suppressed,and the degradation of the electrical conductivity of the Cu ball 1 isalso suppressed. In this executed examples, the lower limit of theVickers hardness may be more than 0 HV, preferably 20 HV or more.

<Alpha Dose of Cu Ball: 0.0200 Cph/Cm² or Lower>

The alpha dose of the Cu ball 1 is preferably 0.0200 cph/cm² or lower.This is alpha dose such that it is insignificant for any soft errors inthe high-density mounting of the electronic components. The alpha doseis more preferably 0.0100 cph/cm² or lower, still more preferably 0.0050cph/cm² or lower, further more preferably 0.0020 cph/cm² or lower, andmost preferably 0.0010 cph/cm² or lower from the viewpoints ofsuppressing the soft error in the further high-density mounting of theelectronic components. In order to suppress any soft errors by the alphadose, the contents of radioactive isotope such as U, Th and the like arepreferably lower than 5 ppb by mass.

<Discoloring Resistance of Cu Ball: 55 or More of Lightness>

The Cu ball 1 preferably has lightness that is 55 or more. The lightnessis referred to as “L* value” of L*a*b* color space. Since the Cu ball 1,on a surface of which a sulfide or a sulfur oxide derived from S isformed, has lower lightness, it is estimated that the formation of thesulfide or the sulfur oxide is sufficiently suppressed when thelightness is 55 or more. In addition, the wettability of the Cu ball 1having lightness of 55 or more when the Cu ball 1 is installed isexcellent. On the contrary, when the Cu ball 1 has lightness of lessthan 55, it is estimated that the formation of the sulfide or the sulfuroxide is not sufficiently suppressed. The sulfide or the sulfur oxideexerts any bad influence upon the Cu ball 1 and its wettabilitydeteriorates when the Cu ball 1 is directly connected to the electrode.The deterioration of the wettability may lead to a generation of acondition that is not wetted or cause a self-alignment property thereofto deteriorate.

<Diameter of Cu Ball: 1 μm or More to 1000 μm or Lower>

A diameter of the Cu ball 1 is preferably 1 μm or more to 1000 μm orlower, more preferably, is 50 μm or more to 300 μm or lower. If thediameter is within this range, the spherical Cu ball 1 can be stablymanufactured. Moreover, a shorted connection can be suppressed when apitch between the terminals is narrow. Here, in a case where the Cu ball1 is used for solder paste, a collection of “Cu balls” can be called as“Cu powder”. In a case where the Cu ball is used for the Cu powder, itis preferable that the diameter of the Cu ball 1 is generally 1-300 μm.

The following will describe a metal layer 2 that covers the Cu ball 1 ineach of the Cu core ball 11A according to the first embodiment of thepresent invention and the Cu core ball 11B according to the secondembodiment of the present invention.

<Metal Layer>

The metal layer 2 is composed of, for example, Ni plating layer, Coplating layer, Fe plating layer, Pd plating layer and plating layer(single layer or multiple layers) including two or more elementsselected from a group of Ni, Co, Fe and Pd. The metal layer 2 is notmelted at a soldering temperature when using the Cu core ball 11A, 11Bfor the solder bump and remains therein, so that the metal layer 2contributes to a height of the solder joint and the Cu core ball isconfigured to have high sphericity and less variation in diameter. Inaddition, from the viewpoints of suppressing the soft error, it isconfigured to reduce the alpha dose.

<Composition and Thickness of Metal Layer>

The metal layer 2 contains Ni, Co, Fe or Pd excluding any inevitableimpurities when the metal layer 2 is composed of Ni, Co, Fe or Pdindependently. The metal to be used for the metal layer 2 is not limitedto an independent metal: Any alloy combining two or more elementsselected from the group of Ni, Co, Fe and Pd may be used therefor. Themetal layer 2 may be configured to have multiple layers. The multiplelayers may be suitable combinations of a layer that is configured tocontain Ni, Co, Fe or Pd independently and an alloy layer combining twoor more elements selected from the group of Ni, Co, Fe and Pd. Inaddition, a second metal layer which is configured to contain metalitself or the alloy thereof other than the element selected from thegroup of Ni, Co, Fe and Pd in the metal layer 2 may cover a surface ofthe metal layer 2. The metal layer 2 and the second metal layer mayinclude a predetermined amount of other element(s) so that it does not(they do not) have any influence upon a barrier function and/or magneticfunction of Ni, Co, Fe and Pd. As the elements to be added, for example,Sn, Ag, Cu, In, Sb, Ge, P and the like are exemplified. The metal layer2 or the second metal layer has thickness of, for example, 1 μm through20 μm.

The following will describe a solder layer 3 that covers the metal layer2 in the Cu core ball 11B according to the second embodiment of thepresent invention.

<Solder Layer>

The solder layer 3 contains a Sn plating layer or an alloy plating layerincluding a main component of Sn.

<Composition and Thickness of Solder Layer>

The solder constituting the solder layer 3 may have solder alloycomposition that includes a main component of Sn in a case of an alloy,but otherwise it is not particularly limited. In addition, as the solderlayer, a Sn plating film may be used. For example, Sn, Sn—Ag alloy,Sn—Cu alloy, Sn—Ag—Cu alloy, Sn—In alloy and an alloy containing themand predetermined alloy element(s) are exemplified. In every case,contents of Sn are 40% by mass or more. As the alloy element to beadded, for example, Ag, Cu, In, Ni, Co, Sb, Ge, P, Fe, Bi, Pb, Zn, Gaand the like are exemplified. Among them, the alloy composition of thesolder layer 3 is preferably Sn-3Ag-0.5Cu alloy from the viewpoints ofthe impact resistance to dropping. Use of the solder having low alphadose in the solder layer 3 may be configured to be the Cu core ball 11Bhaving low alpha dose. The thickness of the solder layer 3 is notparticularly limited, but it is sufficient to be 100 μm or less on oneside only, and it is more preferably to be 20 μm through 50 μm on oneside only.

<Alpha Dose of Cu Core Ball: 0.0200 Cph/Cm² or Lower>

The alpha dose of each of the Cu core balls 11A, 11B according to thefirst and second embodiments of the present invention is 0.0200 cph/cm²or lower. This is alpha dose such that it is insignificant for any softerrors in the high-density mounting of the electronic components. Thealpha dose of the Cu core ball 11A according to the first embodiment ofthe present invention is attained by a fact that the alpha dose of themetal layer 2 constituting the Cu core ball 11A is 0.0200 cph/cm² orlower. Therefore, the Cu core ball 11A according to the first embodimentof the present invention is covered by such metal layer 2 and thus,exhibits low alpha dose. The alpha dose of the Cu core ball 11Baccording to the second embodiment of the present invention is attainedby a fact that the alpha dose of the metal layer 2 and the solder layer3 constituting the Cu core ball 11B is 0.0200 cph/cm² or lower.Therefore, the Cu core ball 11B according to the second embodiment ofthe present invention is covered by the metal layer 2 and the solderlayer 3 and thus, exhibits low alpha dose. The alpha dose thereof ispreferably 0.0100 cph/cm² or lower, it is more preferably 0.0050 cph/cm²or lower, it is further preferably 0.0020 cph/cm² or lower, it is mostpreferably 0.0010 cph/cm² or lower, from the viewpoints of suppressingthe soft error in the further high-density mounting of the electroniccomponents. Contents of U and Th in the metal layer 2 and the solderlayer 3 are respectively 5 ppb by mass or lower because the alpha doseof the Cu ball 1 is 0.0200 cph/cm² or lower. From viewpoints ofsuppressing any soft errors in a present or future high-densitymounting, the contents of U and Th are preferably 2 ppb by mass orlower, respectively.

<Sphericity of Cu Core Ball: 0.95 or Higher>

For the Cu core ball 11A, in which the metal layer 2 covers the Cu ball1, according to the first embodiment of the present invention and the Cucore ball 11B, in which the metal layer 2 and the solder layer 3 coverthe Cu ball 1, according to the second embodiment of the presentinvention, the sphericity thereof is preferably 0.95 or higher, it ismore preferably 0.98 or higher, and it is still more preferably 0.99 orhigher. If the sphericity of each of the Cu core balls 11A, 11B is lessthan 0.95, the Cu core balls 11A, 11B respectively become anindeterminate shape. Therefore, when each of the Cu core balls 11A, 11Bis mounted on an electrode and a reflow treatment is performed thereon,there may be a position gap of each of the Cu core balls 11A, 11B and aself-alignment property thereof becomes worse. If the sphericity of eachof the Cu core balls 11A, 11B is 0.95 or higher, a self-alignmentproperty thereof is maintained when each of the Cu core balls 11A, 11Bis installed on electrode 100 of the semiconductor chip 10. Further,since the Cu ball 1 has sphericity of 0.95 or more and the Cu ball 1 andthe metal layer 2 in the Cu core balls 11A, 11B are not melted at asoldering temperature, any variation in heights of the solder joints50A, 50B is suppressed. This enables the poor joints between thesemiconductor chip 10 and the printed circuit board 40 to be surelyprevented.

<Magnetic Function of Metal Layer>

Since the metal layer 2 composed of ferromagnetic material covers thesurface of the Cu ball 1 in each of the Cu core balls 11A, 11B, the Cucore balls 11A, 11B have magnetism as whole of each of the Cu coreballs. Thus, the Cu core balls 11A, 11B having magnetism exhibit thefollowing effect. Namely, in a case where the Cu core ball 11A, 11B isinstalled on the electrode using a transfer method, magnetic force by amagnet provided in a stage is utilized, so that the Cu core balls 11A,11B spread on a mask mounted on a substrate are appropriatelytransferred into an opening of the mask. This allows the Cu core balls11A, 11B to be prevented from being damaged and/or deformed by thetransfer means or being contaminated because a spatula or a brush as aconventional transfer means does not directly contact any Cu core balls11A, 11B. The alignment property when installing the Cu core ball 11A,11B on the electrode is maintained because an action of the magnetadjusts a position of the Cu core ball 11A, 11B.

<Barrier Function of Metal Layer>

During the reflow, if Cu diffuses from Cu ball 1 to solder paste usedfor connecting the Cu core ball 11A, 11B and the electrode, a largeamount of intermetallic compounds such as Cu₆Sn₅ and Cu₃Sn₅, which aresolid but delicate, may be formed in the solder layer and a connectioninterface. When receiving any impact, a crack may develop, therebydestroying the connection portion. Accordingly, in order to obtainsufficient connection strength, it may be required to suppress thediffusion of Cu from the Cu ball 1 to the solder (Barrier Function). Inthe embodiments, the metal layer 2 functioning as a barrier layer isformed on a surface of the Cu ball 1 so that it is suppress to spread Cufrom the Cu ball 1 to the solder of the solder paste.

<Solder Joint, Solder Paste and Formed Solder>

The solder paste is configured by containing the Cu core ball 11A, 11Bin the solder. The formed solder is configured by spreading the Cu coreball 11A, 11B into solder. The Cu core ball 11A, 11B is used for formingthe solder joint connecting the electrodes.

<Method of Manufacturing Cu Ball>

The following will describe an example of a method of manufacturing theCu ball 1. The Cu material as material thereof is put on a plate havingheat-resisting property (hereinafter, referred to as “heat-resistingplate”) such as ceramics and is heated in a furnace together with theheat-resisting plate. There are many dimples each having a hemisphericbottom in the heat-resisting plate. A diameter of the dimple and a depththereof are suitably set according to a diameter of the Cu ball 1. Forexample, the diameter thereof is 0.8 mm and the depth thereof is 0.88mm. Further, the Cu materials each having a chip shape, which areobtained by cutting a fine wire made of Cu, are put into the dimples oneby one in the heat-resisting plate. The heat-resisting plate in whichthe Cu material have been put into each of the dimples is heated at1100-1300 degrees C. in the furnace into which ammonia decomposition gasis filled and heating process is performed thereon during 30 through 60minutes. In this moment, when temperature in the furnace is more thanthe melting point of Cu, the Cu material is melted so that it becomessphered. Thereafter, the interior of the furnace is cooled and the Cuball 1 is formed by being cooled rapidly in each of the dimples of theheat-resisting plate.

Further, as other methods, there are an atomizing method in which themolten Cu is dropped down from an orifice pierced in a bottom of amelting pot and the droplet is rapidly cooled to a room temperature (25degrees C., for example) to be sphered as the Cu ball 1 and a method inwhich thermal plasma heats cut metal of Cu at a temperature of 1000degrees C. or more to be sphered.

For the method of manufacturing the Cu ball 1, the Cu material as a rawmaterial of the Cu ball 1 may be heated at 800 through 1000 degrees C.before the Cu ball 1 is sphered.

As the Cu material that is a raw material of the Cu ball 1, for example,nugget, wire, plate material or the like can be used. The Cu materialmay have purity of more than 4N5 through not more than 6N from aviewpoint such that the purity in the Cu ball 1 is not too low.

In a case of using a Cu material having the further high purity, theheating treatment mentioned above is not performed and a retentiontemperature of the molten Cu may be lowered to approximately 1000degrees C. as in a conventional way. Thus, the above-mentioned heatingtreatment may be omitted or changed according to the alpha dose or thepurity in the Cu material. In addition, in a case that a Cu ball 1having a high alpha dose or a deformed Cu ball 1 is manufactured, such aCu ball 1 is available for reuse as raw materials so that furthermorethe alpha dose can be decreased.

<Method of Manufacturing Cu Core Ball 11A>

As a method of forming the metal layer 2 on the manufactured Cu ball 1,a known electroplating method or the like may be adopted. When, forexample, a Ni plating layer is formed, a Ni plating solution is adjustedby using Ni metal or Ni metal salt to a series of plating baths of Niand the Cu ball 1 is dipped and deposited to the Ni plating solution, sothat the Ni plating layer is formed on the surface of the Cu ball 1. Asanother method of forming the metal layer 2 such as Ni plating layer, aknown electroless plating method or the like may be adopted.

<Method of Manufacturing Cu Core Ball 11B>

As a method of forming the metal layer 2 and the solder layer 3 on themanufactured Cu ball 1, a known electroplating method or the like may beadopted. When the solder layer 3 of the solder alloy is formed on asurface of the metal layer 2, a Sn plating solution is adjusted by usingSn metal or Sn metal salt to a series of plating baths of Sn alloys andthe Cu ball 1 which has been covered with the metal layer 2 is dippedand deposited, so that the solder layer 3 is formed on the surface ofthe metal layer 2. As another method of forming the solder layer 3, aknown electroless plating method or the like may be adopted.

Executed Examples

The following will describe executed examples of the invention, but theinvention is not limited thereto. The Cu balls of the executed examplesand the comparison examples, each ball having compositions shown inTables 1A, 1B and 2 were manufactured and the sphericity, the Vickershardness, the alpha dose and the discoloring resistance of each of theseCu balls were measured. In addition, the metal layer 2 covered each ofthe Cu balls of the above-mentioned executed examples and comparisonexamples to prepare the Cu core balls of the executed examples and thecomparison examples and the sphericity and the alpha dose of these Cucore balls were measured. In the following Tables, numerals without anyunits indicate ppm by mass or ppb by mass. Particularly, numericalvalues indicating a content ratio of Fe, Ag, Ni, P, S, Sb, Bi, Zn, Al,As, Cd, Pb, In, Sn and Au in the Tables indicate ppm by mass. A mark“<1” indicates that a content ratio of the corresponding impurityelement in the Cu ball is less than 1 ppm by mass. Numerical valuesindicating a content ratio of U and Th in the Tables indicate ppb bymass. A mark “<5” indicates that a content ratio of the correspondingimpurity element in the Cu ball is less than 5 ppb by mass. The “totalamount of impurities” indicates a total ratio of impurity elementscontained in the Cu ball.

<Manufacturing of Cu Ball>

Manufacturing conditions of the Cu balls were examined. The nuggetmaterials as Cu materials which were an example of metal material wereprepared. The Cu materials having the purity of 6N were used in theExecuted Examples 1 through 13 and 22 and the Comparison Examples 1through 12. The Cu materials having the purity of 5N were used in theExecuted Examples 14 through 21. Each Cu material was put into a meltingpot and then, the melting pot was heated up to temperature of 1200degrees C. and this heating process was performed thereon during 45minutes to melt the Cu material. The molten Cu was dropped down from anorifice pierced in the bottom of the melting pot. The generated dropletswere rapidly cooled to a room temperature (18 degrees C.) so as to besphered as the Cu balls. Thus, the Cu balls each having a mean diametershown in the following Tables were manufactured. Although the elementanalysis can be performed with high accuracy using Inductively-coupledPlasma Source Mass Spectrometry (ICP-MS analysis) or Glow Discharge MassSpectrometry (GD-MS analysis), ICP-MS analysis was used therefor in thisexamples.

<Manufacturing of Cu Core Ball>

The Cu core balls of the Executed Examples and the Comparison Exampleswere manufactured using the above-mentioned Cu balls of the ExecutedExamples and the Comparison Examples, each Cu core ball having Niplating layer as the metal layer with thickness of 2 μm on one sideonly.

The following will describe a method of measuring and evaluating thesphericity and the alpha dose of each of the Cu balls and Cu core balls,and the Vickers hardness and the discoloring resistance of each of theCu balls, more in detail.

<Sphericity>

The sphericity of each of the Cu balls and the Cu core balls wasmeasured by CNC image measurement system. Equipment therefor was theultra quick vision, ULTRA QV350-PRO manufactured by MITSUTOYOCorporation.

<Evaluation Criteria of Sphericity>

The evaluation criteria of sphericity of each of the Cu balls and the Cucore balls were shown as follows in each of the following Tables:

A symbol “OOO” indicated that the sphericity was 0.99 or higher;

A symbol “OO” indicated that the sphericity was 0.98 or higher to lessthan 0.99;

A symbol “O” indicated that the sphericity was 0.95 or higher to lessthan 0.98; and

A symbol “X” indicated that the sphericity was less than 0.95.

<Vickers Hardness>

The Vickers hardness of the Cu ball was measured in accordance with“Vickers Hardness Test—Test method JIS Z2244”. Equipment therefor wasmicro Vickers hardness testing machine, AKASHI micro hardness testerMVK-F 12001-Q manufactured by AKASHI Corporation.

<Evaluation Criteria of Vickers Hardness>

The evaluation criteria of Vickers hardness of each of the Cu balls wereshown as follows in each of the following Tables:

A symbol “O” indicated that the Vickers hardness was within a rangewhich was more than 0 HV to 55.5 HV or lower; and

A symbol “X” indicated that the Vickers hardness exceeded 55.5 HV.

<Alpha Dose>

A measurement method of the alpha dose of each of the Cu balls and theCu core balls was as follows. An alpha-ray measurement instrument of agas-flow proportional counter was used to measure the alpha dose. Ameasurement sample was a 300 mm.times.300 mm flat shallow container withthe Cu balls being bedded on a bottom thereof so as not to see thebottom. This measurement sample was put in the alpha-ray measurementinstrument and was remained in an atmosphere of PR-10 gas flow for 24hours, and then the alpha dose was measured. As for the Cu core balls,the alpha dose was measured using the same method.

<Evaluation Criteria of Alpha Dose>

The evaluation criteria of alpha dose of each of the Cu balls and the Cucore balls were shown as follows in each of the following Tables:

A symbol “O” indicated that the alpha dose was 0.0200 cph/cm² or lower;and

A symbol “X” indicated that the alpha dose exceeded 0.0200 cph/cm².

In addition, the PR-10 gas (argon 90% and methane 10%) used for themeasurement was one such that it was kept for a period of three weeks orlonger since a gas bottle was filled with the PR-10 gas. A reason whyusing the gas bottle kept for the period of three weeks or longer isbased on JESD221 of JEDEC STANDARD-Alpha Radiation Measurement inElectronic Materials determined by JEDEC (Joint Electron DeviceEngineering Council) so as not to produce the alpha-ray by radon in theatmospheric air that enters into the gas bottle.

<Discoloring Resistance>

In order to measure the discoloring resistance of the Cu balls, the Cuballs were heated at 200 degrees C. for 420 seconds using a thermostatoven under the atmosphere and were measured about an alteration oflightness thereof. They were evaluated on whether or not they couldsatisfactorily endure aging variation. The lightness of the Cu balls wasobtained from a color value (L*, a*, b*) by measuring spectraltransmittance with the use of CM-3500d Spectrophotometer manufactured byKonica Minolta, following JIS Z 8722 (Methods of colormeasurement-Reflecting and transmitting objects) using D65 light sourcewith 10 degrees field of view. It is to be noted that the color value(L*, a*, b*) is stipulated in JIS Z 8729 (Color specification-CIELAB andCIELUV color spaces). L* indicates lightness, a* indicates redness andb* indicates yellowness.

<Evaluation Criteria of Discoloring Resistance>

The evaluation criteria of discoloring resistance of each of the Cuballs were shown as follows in each of the following Tables:

A symbol “O” indicated that the lightness after 420 seconds was 55 ormore; and

A symbol “X” indicated that the lightness after 420 seconds was lessthan 55.

<Total Evaluation>

The Cu ball which was evaluated as symbols “O”, “OO” or “OOO” in everyevaluation method and evaluation criteria about the sphericity, theVickers hardness, the alpha dose and the discoloring resistance wasevaluated as a symbol “O” in the total evaluation. On the other hand,the Cu ball which was evaluated as symbol “X” in any one of theevaluation method and evaluation criteria about the sphericity, theVickers hardness, the alpha dose and the discoloring resistance wasevaluated as a symbol “X” in the total evaluation.

The Cu core ball which was evaluated as symbols “O”, “OO” or “OOO” inevery evaluation method and evaluation criteria about the sphericity andthe alpha dose was evaluated as a symbol “O” in the total evaluation. Onthe other hand, the Cu core ball which was evaluated as symbol “X” inany one of the evaluation method and evaluation criteria about thesphericity and the alpha dose was evaluated as a symbol “X” in the totalevaluation.

Since the Vickers hardness of the Cu core ball depended on the Niplating layer which was an example of the metal layer, the Vickershardness of the Cu core ball was not evaluated. When in the Cu coreball, the Vickers hardness of the Cu ball is within a range regulated inthe present invention, the impact resistance to dropping of the Cu coreball may be excellent to suppress any cracks, crush of the electrode anddegradation of electric conductivity.

When the Vickers hardness of the Cu ball exceeds the range regulated inthe present invention, the Cu core ball may have low durability to anyexternal stress, so that the Cu core ball cannot address any issue suchthat the impact resistance to dropping gets worse and cracks aregenerated easily.

Accordingly, the Cu core balls using the Cu balls of the ComparisonExamples 8-11, which had the Vickers hardness exceeding 66.6 HV, werenot suitable for the evaluation of the Vickers hardness, so that theywere evaluated as a symbol “X” in the total evaluation.

Since the discoloring resistance of the Cu core ball depended on the Niplating layer which was an example of the metal layer, the discoloringresistance of the Cu core ball was not evaluated. When in the Cu coreball, the lightness of the Cu ball is within a range regulated in thepresent invention, a sulfide or a sulfur oxide on the surface of the Cuball is suppressed and this is suitable for coating by the metal layersuch as the Ni plating layer or the like.

When the lightness of the Cu ball falls below the range regulated in thepresent invention, the sulfide or the sulfur oxide on the surface of theCu ball is not suppressed, so that this is not suitable for coating bythe metal layer such as the Ni plating layer or the like.

Accordingly, the Cu core balls using the Cu balls of the ComparisonExamples 1-6, which had the lightness after 420 seconds of less than 55,were not suitable for the evaluation of the discoloring resistance, sothat they were evaluated as a symbol “X” in the total evaluation.

TABLE 1A EXECUTED EXECUTED EXECUTED EXECUTED EXECUTED EXECUTED ELEMENTEXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 Cu BALL CuBal Bal Bal Bal Bal Bal Fe 5.0 10.0 49.0 50.0 <1 <1 Ag <1 <1 <1 <1 5.010.0 Ni <1 <1 <1 <1 <1 <1 Fe + Ag + Ni 5.0 10.0 49.0 50.0 5.0 10.0 S <1<1 <1 <1 <1 <1 P <1 <1 <1 <1 <1 <1 Sb <1 <1 <1 <1 <1 <1 Bi <1 <1 <1 <1<1 <1 Zn <1 <1 <1 <1 <1 <1 Al <1 <1 <1 <1 <1 <1 As <1 <1 <1 <1 <1 <1 Cd<1 <1 <1 <1 <1 <1 Pb <1 <1 <1 <1 <1 <1 Sn <1 <1 <1 <1 <1 <1 In <1 <1 <1<1 <1 <1 Au <1 <1 <1 <1 <1 <1 U <5 <5 <5 <5 <5 <5 Th <5 <5 <5 <5 <5 <5TOTAL AMOUNT 5.0 10.0 49.0 50.0 5.0 10.0 OF IMPURITIES DIAMETER ϕ 300 μm300 μm 300 μm 300 μm 300 μm 300 μm Cu CORE BALL Ni PLATING  2 μm  2 μm 2 μm  2 μm  2 μm  2 μm LAYER THICKNESS; ONE SIDE: EVALUATION SPHERICITY◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ OF Cu BALL VICKERS ◯ ◯ ◯ ◯ ◯ ◯ HARDNESS ALPHADOSE ◯ ◯ ◯ ◯ ◯ ◯ DISCOLORING ◯ ◯ ◯ ◯ ◯ ◯ RESISTANCE TOTAL ◯ ◯ ◯ ◯ ◯ ◯EVALUATION EVALUATION SPHERICITY ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ OF Cu COREVICKERS — — — — — — BALL HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ ◯ DISCOLORING — —— — — — RESISTANCE TOTAL ◯ ◯ ◯ ◯ ◯ ◯ EVALUATION EXECUTED EXECUTEDEXECUTED EXECUTED EXECUTED EXECUTED ELEMENT EXAMPLE 7 EXAMPLE 8 EXAMPLE9 EXAMPLE 10 EXAMPLE 11 EXAMPLE 12 Cu BALL Cu Bal Bal Bal Bal Bal Bal Fe<1 <1 <1 <1 <1 <1 Ag 49.0 50.0 <1 <1 <1 <1 Ni <1 <1 5.0 10.0 49.0 50.0Fe + Ag + Ni 49.0 50.0 5.0 10.0 49.0 50.0 S <1 <1 <1 <1 <1 <1 P <1 <1 <1<1 <1 <1 Sb <1 <1 <1 <1 <1 <1 Bi <1 <1 <1 <1 <1 <1 Zn <1 <1 <1 <1 <1 <1Al <1 <1 <1 <1 <1 <1 As <1 <1 <1 <1 <1 <1 Cd <1 <1 <1 <1 <1 <1 Pb <1 <1<1 <1 <1 <1 Sn <1 <1 <1 <1 <1 <1 In <1 <1 <1 <1 <1 <1 Au <1 <1 <1 <1 <1<1 U <5 <5 <5 <5 <5 <5 Th <5 <5 <5 <5 <5 <5 TOTAL AMOUNT 49.0 50.0 5.010.0 49.0 50.0 OF IMPURITIES DIAMETER ϕ 300 μm 300 μm 300 μm 300 μm 300μm 300 μm Cu CORE BALL Ni PLATING  2 μm  2 μm  2 μm  2 μm  2 μm  2 μmLAYER THICKNESS; ONE SIDE: EVALUATION SPHERICITY ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯OF Cu BALL VICKERS ◯ ◯ ◯ ◯ ◯ ◯ HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ ◯DISCOLORING ◯ ◯ ◯ ◯ ◯ ◯ RESISTANCE TOTAL ◯ ◯ ◯ ◯ ◯ ◯ EVALUATIONEVALUATION SPHERICITY ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ OF Cu CORE VICKERS — — — —— — BALL HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ ◯ DISCOLORING — — — — — —RESISTANCE TOTAL ◯ ◯ ◯ ◯ ◯ ◯ EVALUATION

TABLE 1B EXECUTED EXECUTED EXECUTED EXECUTED EXECUTED ELEMENT EXAMPLE 13EXAMPLE 14 EXAMPLE 15 EXAMPLE 16 EXAMPLE 17 Cu BALL Cu Bal Bal Bal BalBal Fe 5.0 1.7 1.7 2.5 2.3 Ag 5.0 10.1 9.3 9.5 10.7 Ni 5.0 3.8 4.2 0.81.2 Fe + Ag + Ni 15.0 15.6 15.2 12.8 14.2 S <1 <1 <1 <1 <1 P <1 <1 <1 <1<1 Sb <1 <1 <1 <1 <1 Bi <1 <1 <1 <1 <1 Zn <1 <1 <1 <1 <1 Al <1 <1 <1 <1<1 As <1 <1 <1 <1 <1 Cd <1 <1 <1 <1 <1 Pb <1 <1 <1 <1 <1 Sn <1 <1 <1 <1<1 In <1 <1 <1 <1 <1 Au <1 <1 <1 <1 <1 U <5 <5 <5 <5 <5 Th <5 <5 <5 <5<5 TOTAL AMOUNT 15.0 15.6 15.2 12.8 14.2 OF IMPURITIES DIAMETER ϕ 300 μm300 μm 300 μm 300 μm 300 μm Cu CORE BALL Ni PLATING  2 μm  2 μm  2 μm  2μm  2 μm LAYER THICKNESS: ONE SIDE EVALUATION SPHERICITY ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯◯◯◯ OF Cu BALL VICKERS ◯ ◯ ◯ ◯ ◯ HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯DISCOLORING ◯ ◯ ◯ ◯ ◯ RESISTANCE TOTAL ◯ ◯ ◯ ◯ ◯ EVALUATION EVALUATIONSPHERICITY ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ OF Cu CORE VICKERS — — — — — BALLHARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ DISCOLORING — — — — — RESISTANCE TOTAL ◯ ◯◯ ◯ ◯ EVALUATION EXECUTED EXECUTED EXECUTED EXECUTED EXECUTED ELEMENTEXAMPLE 18 EXAMPLE 19 EXAMPLE 20 EXAMPLE 21 EXAMPLE 22 Cu BALL Cu BalBal Bal Bal Bal Fe 2.3 2.3 2.3 5.8 5.5 Ag 10.7 10.7 10.7 <1 10.1 Ni 1.21.2 1.2 <1 5.7 Fe + Ag + Ni 14.2 14.2 14.2 5.8 21.3 S <1 <1 <1 <1 <1 P<1 <1 <1 <1 2.9 Sb <1 <1 <1 <1 <1 Bi <1 <1 <1 <1 <1 Zn <1 <1 <1 <1 <1 Al<1 <1 <1 <1 <1 As <1 <1 <1 <1 <1 Cd <1 <1 <1 <1 <1 Pb <1 <1 <1 13.2 <1Sn <1 <1 <1 30.3 <1 In <1 <1 <1 <1 <1 Au <1 <1 <1 <1 <1 U <5 <5 <5 <5 <5Th <5 <5 <5 <5 <5 TOTAL AMOUNT 14.2 14.2 14.2 49.3 24.2 OF IMPURITIESDIAMETER ϕ 200 μm 100 μm 50 μm 50 μm 300 μm Cu CORE BALL Ni PLATING  2μm  2 μm  2 μm  2 μm  2 μm LAYER THICKNESS: ONE SIDE EVALUATIONSPHERICITY ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ OF Cu BALL VICKERS ◯ ◯ ◯ ◯ ◯ HARDNESSALPHA DOSE ◯ ◯ ◯ ◯ ◯ DISCOLORING ◯ ◯ ◯ ◯ ◯ RESISTANCE TOTAL ◯ ◯ ◯ ◯ ◯EVALUATION EVALUATION SPHERICITY ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ OF Cu CORE VICKERS— — — — — BALL HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ DISCOLORING — — — — —RESISTANCE TOTAL ◯ ◯ ◯ ◯ ◯ EVALUATION

TABLE 2 COMPAR- COMPAR- COMPAR- COMPAR- COMPAR- COMPAR- ISON ISON ISONISON ISON ISON ELEMENT EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE 5EXAMPLE 6 Cu BALL Cu Bal Bal Bal Bal Bal Bal Fe <1 <1 <1 <1 <1 <1 Ag <1<1 <1 <1 <1 <1 Ni <1 <1 <1 <1 <1 <1 Fe + Ag + Ni 0.0 0.0 0.0 0.0 0.0 0.0S 10.0 15.0 20.0 25.0 30.0 35.0 P <1 <1 <1 <1 <1 <1 Sb <1 <1 <1 <1 <1 <1Bi <1 <1 <1 <1 <1 <1 Zn <1 <1 <1 <1 <1 <1 Al <1 <1 <1 <1 <1 <1 As <1 <1<1 <1 <1 <1 Cd <1 <1 <1 <1 <1 <1 Pb <1 <1 <1 <1 <1 <1 Sn <1 <1 <1 <1 <1<1 In <1 <1 <1 <1 <1 <1 Au <1 <1 <1 <1 <1 <1 U <5 <5 <5 <5 <5 <5 Th <5<5 <5 <5 <5 <5 TOTAL AMOUNT 10.0 15.0 20.0 25.0 30.0 35.0 OF IMPURITIESDIAMETER ϕ 300 μm 300 μm 300 μm 300 μm 300 μm 300 μm Cu CORE BALL NiPLATING  2 μm  2 μm  2 μm  2 μm  2 μm  2 μm LAYER THICKNESS: ONE SIDEEVALUATION SPHERICITY ◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ OF Cu BALL VICKERS ◯ ◯ ◯ ◯◯ ◯ HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ ◯ DISCOLORING X X X X X X RESISTANCETOTAL X X X X X X EVALUATION EVALUATION SPHERICITY ◯◯ ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯◯◯◯ OF Cu CORE VICKERS — — — — — — BALL HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ ◯DISCOLORING — — — — — — RESISTANCE TOTAL X X X X X X EVALUATION COMPAR-COMPAR- COMPAR- COMPAR- COMPAR- COMPAR- ISON ISON ISON ISON ISON ISONELEMENT EXAMPLE 7 EXAMPLE 8 EXAMPLE 9 EXAMPLE 10 EXAMPLE 11 EXAMPLE 12Cu BALL Cu Bal Bal Bal Bal Bal Bal Fe <1 50.0 4.2 52.0 5.7 1.2 Ag <150.0 29.1 51.7 30.5 <1 Ni <1 50.0 14.7 49.9 12.3 <1 Fe + Ag + Ni 0.0150.0 48.0 153.6 48.5 1.2 S <1 <1 <1 <1 <1 <1 P <1 <1 211.5 10.2 199.9<1 Sb <1 <1 23.3 20.5 <1 <1 Bi <1 <1 51.9 17.9 <1 <1 Zn <1 13.0 5.7 <1<1 <1 Al <1 <1 <1 <1 <1 <1 As <1 <1 51.2 <1 <1 <1 Cd <1 <1 6.5 <1 <1 <1Pb <1 11.2 31.4 <1 <1 <1 Sn <1 151.0 58.7 <1 <1 <1 In <1 <1 <1 <1 <1 <1Au <1 <1 <1 <1 <1 <1 U <5 <5 <5 <5 <5 <5 Th <5 <5 <5 <5 <5 <5 TOTALAMOUNT 0.0 325.2 488.2 202.2 248.4 1.2 OF IMPURITIES DIAMETER ϕ 300 μm300 μm 300 μm 300 μm 300 μm 300 μm Cu CORE BALL Ni PLATING  2 μm  2 μm 2 μm  2 μm  2 μm  2 μm LAYER THICKNESS: ONE SIDE EVALUATION SPHERICITYX ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ X OF Cu BALL VICKERS ◯ X X X X ◯ HARDNESS ALPHA DOSE ◯◯ ◯ ◯ ◯ ◯ DISCOLORING ◯ ◯ ◯ ◯ ◯ ◯ RESISTANCE TOTAL X X X X X XEVALUATION EVALUATION SPHERICITY X ◯◯◯ ◯◯◯ ◯◯◯ ◯◯◯ X OF Cu CORE VICKERS— — — — — — BALL HARDNESS ALPHA DOSE ◯ ◯ ◯ ◯ ◯ ◯ DISCOLORING — — — — — —RESISTANCE TOTAL X X X X X X EVALUATION

As shown in Tables 1A and 1B, all of the Cu balls of the executedexamples, having the purity which was 4N5 or higher to 5N5 or lower andthe Cu core balls in which the Ni plating layers covered the Cu balls ofthe executed examples exhibited excellent results in their totalevaluations. Therefore, it has been understood that the purity of the Cuball is preferably 4N5 or higher to 5N5 or lower.

As shown in the Executed Examples 1 through 12 and 21, the Cu ballsthereof, having the purity which was 4N5 or higher to 5N5 or lower andcontaining Fe, Ag or Ni in an amount of 5.0 ppm by mass or more to 50.0ppm by mass or lower and the Cu core balls in which the Ni platinglayers covered the Cu balls of such Executed Examples exhibitedexcellent results in their total evaluations. As shown in the ExecutedExamples 13 through 20 and 22, the Cu balls thereof, having the puritywhich was 4N5 or higher to 5N5 or lower and containing Fe, Ag and Ni ina total amount of 5.0 ppm by mass or more to 50.0 ppm by mass or lowerand the Cu core balls in which the Ni plating layers covered the Cuballs of such Executed Examples exhibited excellent results in theirtotal evaluations. In addition, not shown in the Tables, the Cu ballschanging content of Fe to be 0 ppm by mass or higher to less than 5.0ppm by mass, content of Ag to be 0 ppm by mass or higher to less than5.0 ppm by mass, and content of Ni to be 0 ppm by mass or higher to lessthan 5.0 ppm by mass, from those of the Executed Examples 1 and 18through 22 and containing Fe, Ag and Ni in a total amount of 5.0 ppm bymass or more and the Cu core balls in which the Ni plating layerscovered the Cu balls of such Executed Examples also exhibited excellentresults in their total evaluations.

As shown in the Executed Example 21, the Cu balls containing Fe, Ag orNi in an amount of 5.0 ppm by mass or higher to 50.0 ppm by mass orlower and containing other impurity elements such as Sb, Bi, Zn, Al, As,Cd, Pb, In, Sn and Au in an amount of 50.0 ppm by mass or less,respectively and the Cu core balls in which the Ni plating layerscovered the Cu balls of such an Executed Example also exhibitedexcellent results in the total evaluation thereof.

On the contrary, the Cu ball of the Comparison Example 7 containing Fe,Ag and Ni in a total amount of less than 5.0 ppm by mass, containing Uand Th in an amount of less than 5 ppb by mass and containing otherimpurity elements in an amount of less than 1 ppm by mass and the Cucore balls in which the Ni plating layers covered the Cu balls of such aComparison Example 7 exhibited the sphericity of less than 0.95.Moreover, the Cu ball of the Comparison Example 12 containing anyimpurity elements but containing at least one element selected from thegroup of Fe, Ag and Ni in a total amount of less than 5.0 ppm by mass,and the Cu core balls in which the Ni plating layers covered the Cuballs of such a Comparison Example 12 also exhibited the sphericity ofless than 0.98. From these results, it has been understood that the Cuball containing at least one element selected from the group of Fe, Agand Ni in a total amount of less than 5.0 ppm by mass, and the Cu coreballs in which the Ni plating layers covered such a Cu ball do notrealize any high sphericity.

The Cu ball of the Comparison Example 10 containing Fe, Ag and Ni in atotal amount of 153.6 ppm by mass and other impurity elements in anamount of 50 ppm by mass or lower had Vickers hardness exceeding 55.5HV, so that it did not exhibit any excellent results. The Cu ball of theComparison Example 8 containing Fe, Ag and Ni in a total amount of 150.0ppm by mass or more and other impurity elements in an amount of largelyexceeding 50.0 ppm by mass, particularly Sn in an amount of 151.0 ppm bymass, had the Vickers hardness exceeding 55.5 HV, so that it did notalso exhibit any excellent results. Therefore, it has been understoodthat even when the Cu ball has the purity which is 4N5 or more to 5N5 orlower, if the Cu ball contains at least one element selected from thegroup of Fe, Ag and Ni in a total amount exceeding 50.0 ppm by mass, theCu ball has large Vickers hardness, thereby failing to realize lowhardness. Thus, when the Vickers hardness of the Cu ball exceeds therange regulated in the present invention, the Cu ball may have lowdurability to any external stress, so that the Cu core ball cannotaddress any issue such that the impact resistance to dropping gets worseand cracks are generated easily. In addition, it has been estimated thatthe Cu ball preferably contains respective other impurity elements in arange of not exceeding 50.0 ppm by mass.

From these results, it has been understood that the Cu ball having thepurity which was 4N5 or higher to 5N5 or lower and containing at leastone element selected from the group of Fe, Ag and Ni in a total amountof 5.0 ppm by mass or more to 50.0 ppm by mass or lower realizes highsphericity and low hardness, and suppresses discoloration. The Cu coreball in which the Ni plating layer covers such a Cu ball realizes highsphericity. In addition, since the Cu ball realizes low hardness, the Cucore ball is also excellent for the impact resistance to dropping tosuppress any cracks, thereby suppressing a crash of electrode and thelike and the degradation of the electrical conductivity thereof. Sincethe discoloration of the Cu ball is suppressed, this is suitable for thecoating by the metal layer such as the Ni plating layer or the like. Itis preferable that contents of other impurity elements are respectively50.0 ppm by mass or lower.

The Cu balls of the Executed Examples 17 through 20 had the samecomposition but different diameters. They all exhibited excellentresults in their total evaluations. The Cu core balls in which the Niplating layer covered the Cu balls of the Executed Examples 17 through20 all also exhibited excellent results in their total evaluations. TheCu balls each having the same composition as those of the ExecutedExamples and having a diameter which is 1 μm or larger to 1000 μm orlower, not shown in the Tables, all exhibited excellent results in theirtotal evaluations. Therefore, it has been understood that the diameterof the Cu ball is preferably 1 μm or larger to 1000 μm or lower,particularly, it is more preferably 50 μm or larger to 300 μm or lower.

The Cu ball of the Executed Example 22 containing Fe, Ag and Ni in atotal amount of 5.0 ppm by mass or more to 50.0 ppm by mass or lower andP in an amount of 2.9 ppm by mass exhibited excellent results in thetotal evaluation thereof. The Cu core ball in which the Ni plating layercovers the Cu ball of the Executed Example 22 also exhibited excellentresults. The Cu ball of the Comparison Example 11 containing Fe, Ag andNi in a total amount of 50.0 ppm by mass or less, which is similar tothe Cu ball of the Executed Example 22, had the Vickers hardnessexceeding 55.5 HV, so that it exhibited a result that is different fromthat of the Cu ball of the Executed Example 22. The Cu ball of theComparison Example 9 also had the Vickers hardness exceeding 55.5 HV.This is because the Cu balls of the Comparison Examples 9 and 11 containa large amount of P. From this result, it has been understood that whenincreasing a content of P, the Vickers hardness becomes large.Therefore, it has been understood that the content of P in the Cu ballis preferably less than 3 ppm by mass, particularly, it is morepreferably less than 1 ppm by mass.

The Cu balls and the Cu core balls of the Executed Examples exhibitedalpha dose of 0.0200 cph/cm² or lower. Therefore, when using the Cuballs and Cu core balls of the Executed Examples in the high-densitymounting of the electronic components, it may be suppress any softerrors.

The Cu ball of the Comparison Example 7 exhibited excellent resultsabout the discoloring resistance while the Cu balls of the ComparisonExamples 1 through 6 did not exhibit any excellent results about thediscoloring resistance. When comparing each of the Cu balls of theComparison Examples 1 through 6 with the Cu ball of the ComparisonExample 7, there was only a difference in the content of S on theircompositions. Therefore, it has been understood that in order to obtainan excellent result of the discoloring resistance, the content of S maybe required to be less than 1 ppm by mass. Because the Cu balls of allof the Executed Examples contained S of less than 1 ppm by mass, it hasbeen understood that the content of S is preferably less than 1 ppm bymass.

The following will describe a relationship between content of S and thediscoloring resistance. In order to confirming this relationship, the Cuballs of the Executed Example 14 and the Comparison Examples 1 and 5were heated at 200 degrees C. but these Cu balls were photographedbefore the heating, at 60 seconds after the heating, at 180 secondsafter the heating and at 420 seconds after the heating. The lightness ofeach of the photographed Cu balls was measured. Table 3 indicates therelationship between a period of time when the Cu balls are heated andlightness and FIG. 5 shows a graph of this relationship.

TABLE 3 200° C.-HEATING Ini TIME [sec] No. 0 60 180 420 EXECUTED EXAMPLE14 64.2 64.0 62.8 55.1 COMPARISON EXAMPLE 1 63.8 63.8 61.1 49.5COMPARISON EXAMPLE 5 65.1 63.2 60.0 42.3

From this Table 3, in a case of comparing the lightness of the Cu ballsbefore the heating with the lightness of the Cu balls at 420 secondsafter the heating, the lightness of each of the Cu balls of the ExecutedExample 14 and the Comparison Examples 1 and 5 exhibited values near 64or 65 before the heating. At 420 seconds after the heating, however, theCu ball of the Comparison Example 5 containing S of 30.0 ppm by massexhibited the lowest lightness, the Cu ball of the Comparison Example 1containing S of 10.0 ppm by mass exhibited the lower lightness, and theCu ball of the Executed Example 14 containing S of less than 1 ppm bymass exhibited the low lightness. Therefore, it has been understood thatthe more the content of S is, the less the lightness after the heatingis. Since the Cu balls of the Comparison Examples 1 and 5 exhibited thelightness below 55, it has been understood that the Cu ball containing Sof 10.0 ppm by mass or more forms a sulfide or a sulfur oxide whenheating the Cu ball, so that it is easy to discolor. When the Cu ballcontains S within a range from 0 ppm by mass or more to 1.0 ppm by massor lower, it has been understood that the Cu ball suppresses formationof the sulfide or the sulfur oxide, thereby enabling wettability thereofto be improved. It is to be noted that when installing the Cu ball ofthe Executed Example 14 on the electrode, the Cu ball exhibited goodwettability.

The Cu balls of these Executed Examples, which have the purity which is4N5 or higher to 5N5 or lower, contains at least one element selectedfrom a group of Fe, Ag and Ni in a total amount of 5.0 ppm by mass ormore to 50.0 ppm by mass or lower, contains S in an amount of 0 ppm bymass or more to 1.0 ppm by mass or lower and P in an amount of 0 ppm bymass or more to less than 3.0 ppm by mass, all exhibited sphericitywhich is 0.98 or higher, thereby realizing high sphericity. Therealization of the high sphericity allows the self-alignment propertywhen installing the Cu ball on the electrode to be maintained and allowsvariation of the heights of the Cu balls to be suppressed. The sameeffect is obtained in the Cu core balls in which the metal layer coverseach of the Cu balls of the Executed Examples and the Cu core balls inwhich the solder layer further covers the metal layer.

Since the Cu balls of the Executed Examples all exhibited the Vickershardness of 55 HV or less, they realize low hardness. By realizing thelow hardness, it is possible to improve the impact resistance todropping of the Cu ball. The realization of low hardness in the Cu ballenables the Cu core balls in which the metal layer covers each of the Cuballs of the Executed Examples and the Cu core balls in which the solderlayer further covers the metal layer to be made the impact resistance todropping thereof excellent, thereby suppressing any cracks, a crash ofelectrode and the like and the degradation of the electricalconductivity thereof.

In addition, the discoloration was suppressed in all of the Cu balls ofthe Executed Examples. By suppressing the discoloration of the Cu balls,it is possible to suppress a bad influence upon the Cu ball based on thesulfide or the sulfur oxide and improve the wettability the Cu ball whenit is installed on the electrode. By the suppression of thediscoloration of the Cu ball, this is suitable for coating with themetal layer such as the Ni plating layer or the like.

Further, although as the Cu material of the Executed Examples, the Cuballs having the purity of 4N5 or more and 5N5 or lower have beenmanufactured using the Cu nugget material having the purity exceeding4N5 to 6N or lower, both of the Cu balls and the Cu core balls exhibitedexcellent results in their total evaluations when using the wirematerial or plate material having the purity exceeding 4N5 to 6N orlower.

The description of the various embodiments of the present invention havebeen presented for purposes of illustration, but are not intended to beexhaustive or limited to the embodiments disclosed. Many modificationsand variations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A Cu core ball comprising: a Cu ball, and one ormore metal layer for covering a surface of the Cu ball, each layerincluding one or more element selected from a group of Ni, Co, Fe andPd, wherein the Cu ball contains at least one element selected from agroup of Fe, Ag and Ni in a total amount of 5.0 ppm by mass or more to50.0 ppm by mass or lower, S in an amount of 0 ppm by mass or more to1.0 ppm by mass or lower, P in an amount of 0 ppm by mass or more toless than 3.0 ppm by mass, and remainder of Cu and inevitableimpurities, wherein the Cu ball contains purity which is 99.995% by massor higher to 99.9995% by mass or lower, and sphericity which is 0.95 orhigher, and wherein the Cu ball contains a diameter of 1 μm or more to1000 μm or lower.
 2. The Cu core ball according to claim 1 wherein thesphericity thereof is 0.98 or higher.
 3. The Cu core ball according toclaim 1 wherein the sphericity thereof is 0.99 or higher.
 4. The Cu coreball according to claim 1 wherein the Cu core ball contains alpha dosewhich is 0.0200 cph/cm² or lower.
 5. The Cu core ball according to claim1 wherein the Cu core ball contains alpha dose which is 0.0010 cph/cm²or lower.
 6. The Cu core ball according to claim 1, further containing asolder layer which covers a surface of the metal layer wherein thesphericity thereof is 0.95 or higher.
 7. The Cu core ball according toclaim 6 wherein the sphericity thereof is 0.98 or higher.
 8. The Cu coreball according to claim 6 wherein the sphericity thereof is 0.99 orhigher.
 9. The Cu core ball according to claim 6 wherein the Cu coreball contains alpha dose which is 0.0200 cph/cm² or lower.
 10. The Cucore ball according to claim 6 wherein the Cu core ball contains alphadose which is 0.0010 cph/cm² or lower.
 11. A solder joint using the Cucore ball according to claim
 1. 12. The solder joint according to claim1, the Cu are ball further containing a solder layer which covers asurface of the metal layer wherein the sphericity thereof is 0.95 orhigher.
 13. Solder paste using the Cu core ball according to claim 1.14. The solder paste according to claim 13, the Cu core ball furthercontaining a solder layer which covers a surface of the metal layerwherein the sphericity thereof is 0.95 or higher.
 15. Formed solderusing the Cu core ball according to claim
 1. 16. The formed solderaccording to claim 15, the Cu core ball further containing a solderlayer which covers a surface of the metal layer wherein the sphericitythereof is 0.95 or higher.